1. Field of the Invention
The present invention relates to an azo compound, a curable composition containing the azo compound, a color filter using the curable composition, and a method of producing the color filter.
2. Description of the Related Art
A pigment dispersion method has been employed as one method of forming a color filter for use in a liquid crystal display element, a solid state imaging device, etc. An example of the pigment dispersion method is a method of producing a color filter by a photolithographic method using a color radiation-sensitive composition prepared by dispersing a pigment in any of various light-sensitive compositions. The method is stable to light, heat, and the like because a pigment is used, and the positional accuracy of patterning can be secured because a photolithographic method is used to carry out patterning. Therefore, the pigment dispersion method has been widely used as a method suitable for producing a color filter for a color display having a large screen and high precision.
When a color filter is produced by the pigment dispersion method, the radiation-sensitive composition is applied to a substrate by, for example, a spin coater or roll coater, and then dried to form a coating layer. Then, the coating layer is subjected to pattern exposure and developed to form color pixels. By repeating the operation for every color, a color filter can be obtained.
In the meantime, it has been desired in recent years to develop a higher resolution color filter for use in a solid state imaging device. However, in a conventional pigment dispersion method, it is difficult to further improve resolution and also, the conventional method has, for example, a problem in that coarse particles of a pigment cause color unevenness. Therefore, the pigment dispersion method is not suitable to applications, such as a solid state imaging device, for which fine patterns are required.
In order to achieve the high resolution, it has been studied to use a dye as a coloring material (e.g., Japanese Patent Application Laid-Open (JP-A) No. 6-75375). However, it is known that a dye-containing curable composition has the following problems:    (1) Dyes are usually inferior in light fastness and heat resistance compared to pigments;    (2) It is difficult to obtain a liquid curable composition having a desired spectrum because general dyes are have low solubility in an aqueous alkali solution or an organic solvent (hereinafter sometimes simply referred to as a solvent);    (3) It is difficult to control solubility (development properties) of a cured portion and uncured portion because many dyes interact with other components contained in a curable composition; and    (4) Since a large amount of dyes must be added when the molar extinction coefficient (ε) of the dye is low, it is inevitable to decrease other components in the curable composition, such as a polymerizable compound (monomer), a binder and a photoinitiator, giving rise to problems in that the curability of the composition, heat resistance after curing, and the development properties of a cured or non-cured portion are deteriorated.
Due to the above-described problems, it has been difficult to form a fine and thin color pattern for use in a high resolution color filter. Moreover, unlike the case in which the color pattern is used to produce a semiconductor, the color pattern is required to be in the form of a thin layer having a thickness of 1 μm or less when it is used to produce a color filter for a solid state imaging device. Therefore, a dye having a high molar extinction coefficient (ε) has been demanded so as to achieve a desired absorption even when the layer is thin.
Moreover, dyes used for various uses are generally demanded to have commonly the following properties: desirable absorption properties in terms of color reproducibility; fastness in the environmental conditions in which the dyes are to be used, such as excellent heat resistance, excellent light fastness, and excellent moisture resistance; and high molar extinction coefficient.
In order to solve the above-described problems, various azo dyes have been conventionally widely examined.(e.g., JP-A No. 59-30509, JP-A No. 11-209673, Japanese Patent No. 3020660, JP-A No. 49-74718, Japanese Patent Publication (JP-B) No. 7-11485, JP-A No. 2002-14220, JP-A No. 2002-14223, JP-A No. 2007-41050, and JP-A No. 2007-41076)